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MRI of Perianal Crohn's Disease

¹ Both authors: Department of Radiology, Academic Medical Center Amsterdam, Meibergdreef 9, Amsterdam 1105 AZ, The Netherlands.

View larger version (127K): [in a new window]   Fig. 1A. —Healthy 35-year-old woman. C = endoanal coil. Coronal T2-weighted endoanal image shows normal sphincter anatomy with relatively hyperintense internal sphincter (I) and hypointense external sphincter (E). Puborectalis muscle (P) joins levator plate (L) superiorly. Shape of puborectalis muscle shown is physiologic variation. Often puborectalis muscle is more closely fused with external sphincter (Fig. 6B). Fat-containing ischioanal space (IAS) is hyperintense.

View larger version (135K): [in a new window]   Fig. 1B. —Healthy 35-year-old woman. C = endoanal coil. Axial T2-weighted endoanal image shows normal anatomy of sphincter complex; external (E) and internal (I) sphincters are distinguishable from each other because of substantial contrast difference. Fat-containing intersphincteric space (ISS) is bright on this T2-weighted image (short arrow), whereas longitudinal muscle layer (LML) situated in intersphincteric space is hypointense (long arrow).

View larger version (136K): [in a new window]   Fig. 2A. —14-year-old boy with suspected Crohn's disease and perianal fistula. G = gluteus muscle. Axial T2-weighted image shows fistula caudally from anal sphincter coursing from perineum to scrotum. Tract (arrows) is hardly visible because of equal signal intensities of fistula and surrounding fat.

View larger version (161K): [in a new window]   Fig. 2B. —14-year-old boy with suspected Crohn's disease and perianal fistula. G = gluteus muscle. On axial fat-saturated T2-weighted image obtained at same level as A, diagnosis is much easier to make because brightness of fluid-filled fistula (arrows) stands out against suppressed fat.

View larger version (117K): [in a new window]   Fig. 3A. —29-year-old man with long-standing Crohn's disease. G = gluteus muscle, IO = internal obturator muscle. Axial fat-saturated T2-weighted image shows large horseshoe-shaped structure (arrows). Typical horseshoe abscess extends on both sides of anal midline and has one internal opening, but this abscess extends both superiorly and inferiorly relative to levator ani muscle. Abscess shown has infralevatoric location (abscess shown in Figs. 10A and 10B has supralevatoric location).

View larger version (173K): [in a new window]   Fig. 3B. —29-year-old man with long-standing Crohn's disease. G = gluteus muscle, IO = internal obturator muscle. Axial fat-saturated T1-weighted image after administration of IV contrast medium shows structure, with larger part of it fully enhanced (long arrow) indicating presence of inflammatory tissue. Right leg of structure however only shows partial enhancement of rim (short arrow), indicating presence of fluid in center with rim of inflammatory tissue.

View larger version (156K): [in a new window]   Fig. 4A. —43-year-old man with extensive Crohn's disease who underwent proctocolectomy with creation of ileostomy. G = gluteus muscle, B = bladder. Axial T2-weighted image shows hyperintense collection (arrow).

View larger version (120K): [in a new window]   Fig. 4B. —43-year-old man with extensive Crohn's disease who underwent proctocolectomy with creation of ileostomy. G = gluteus muscle, B = bladder. Axial fat-saturated T2-weighted image shows hyperintense structure (arrow) indicating this could either be fluid-filled lesion (i.e., abscess) or granulation tissue.

View larger version (117K): [in a new window]   Fig. 4C. —43-year-old man with extensive Crohn's disease who underwent proctocolectomy with creation of ileostomy. G = gluteus muscle, B = bladder. Axial fat-saturated T1-weighted image obtained after administration of IV contrast medium shows strong enhancement of rim of lesion, whereas core does not enhance, indicating presence of fluid in center with rim of inflammatory tissue (arrow).

View larger version (154K): [in a new window]   Fig. 5A. —20-year-old woman with long-standing Crohn's disease who had undergone seton placement for anovaginal fistula. E = external sphincter, C = endoanal coil. Axial T2-weighted endoanal image shows anovaginal fistula (long arrow) coursing into anal canal (short arrow). Seton can be seen as hypointense structure within hyperintense tract. I = internal sphincter.

View larger version (106K): [in a new window]   Fig. 5B. —20-year-old woman with long-standing Crohn's disease who had undergone seton placement for anovaginal fistula. E = external sphincter, C = endoanal coil. Axial T2-weighted endoanal image obtained inferior to A shows two branches (arrows) of anovaginal fistula. I = internal sphincter.

View larger version (147K): [in a new window]   Fig. 5C. —20-year-old woman with long-standing Crohn's disease who had undergone seton placement for anovaginal fistula. E = external sphincter, C = endoanal coil. Sagittal T2-weighted image clearly shows path of anovaginal fistula (arrows). E = external sphincter, P = puborectalis muscle, L = levator ani muscle.

View larger version (174K): [in a new window]   Fig. 6A. —33-year-old man with Crohn's disease who exhibited distinct perianal fistulas and abscesses despite infliximab treatment. G = gluteus muscle. Axial T2-weighted image shows three fistulas. Fistulas on right at 7-o'clock position (short arrow) and on left at 3-o'clock position (curved arrow) are classified as transsphincteric. They both track through external sphincter (E) into intersphincteric space. Fistula located dorsally in midline (12-o'clock position, long arrow) at this point courses outside sphincter complex and extends through external sphincter at more superior level (not shown).

View larger version (186K): [in a new window]   Fig. 6B. —33-year-old man with Crohn's disease who exhibited distinct perianal fistulas and abscesses despite infliximab treatment. G = gluteus muscle. Coronal T2-weighted image shows two of three fistulas (arrows). This sequence shows intersphincteric course of transsphincteric fistulas. IO = internal obturator muscle, L = levator ani muscle.

View larger version (97K): [in a new window]   Fig. 7. —Diagram of fistula in ano. Extrasphincteric fistula (Es) tracks outside of external anal sphincter and penetrates levator ani muscle into rectum. Transsphincteric fistula (Ts) tracks from intersphincteric space through external anal sphincter. Superficial fistula (Sf) tracks below both internal and external anal sphincter. Intersphincteric fistula (Is) tracks between internal and external anal sphincters in intersphincteric space. Suprasphincteric fistula (Ss) leaves intersphincteric space over top of puborectalis muscle and penetrates levator ani muscle before tracking to skin.

View larger version (183K): [in a new window]   Fig. 8. —21-year-old man with complex fistulating Crohn's disease. Coronal T2-weighted image shows "high" transsphincteric fistula (solid arrow), meaning that internal sphincter is penetrated at level higher than dentate line. Internal opening into rectum (R) is not clearly visible but most probably is at level of levator ani muscle (L). Inferior part of tract is composed of scar tissue (open arrow). B = bladder, G = gluteus muscle, IO = internal obturator muscle.

View larger version (177K): [in a new window]   Fig. 9A. —33-year-old man who underwent proctocolectomy and pouch reconstruction for Crohn's disease with symptoms indicating presence of abscess despite earlier incision and drainage. Axial T2-weighted image shows large abscess (A) displacing sphincter complex to left and extending into right gluteus muscle (open arrow). In left buttock, another abscess can be seen (solid arrow) in ischioanal fat adjoining gluteus muscle (G).

View larger version (188K): [in a new window]   Fig. 9B. —33-year-old man who underwent proctocolectomy and pouch reconstruction for Crohn's disease with symptoms indicating presence of abscess despite earlier incision and drainage. Axial fat-saturated T2-weighted image shows abscess (A) more clearly because bright signal of fat, in which abscess is located, is suppressed. Abscess on left (arrow) is also more prominently seen than on A. G = gluteus muscle.

View larger version (145K): [in a new window]   Fig. 9C. —33-year-old man who underwent proctocolectomy and pouch reconstruction for Crohn's disease with symptoms indicating presence of abscess despite earlier incision and drainage. Axial fat-saturated T1-weighted image after administration of IV contrast medium clearly shows rim enhancement of lesions on left (arrow) and right (A), indicating presence of large amount of pus. G= gluteus muscle.

View larger version (169K): [in a new window]   Fig. 10A. —29-year old man with Crohn's disease (same patient shown in Figs. 3A, 3B). G = gluteus muscle. Axial T2-weighted image shows supralevatoric location of horseshoe abscess (arrows). IO = internal obturator muscle.

View larger version (149K): [in a new window]   Fig. 10B. —29-year old man with Crohn's disease (same patient shown in Figs. 3A, 3B). G = gluteus muscle. Axial fat-saturated T2-weighted image shows abscess (arrows), but exact size and location are more conspicuous because of suppression of surrounding fat. IO = internal obturator muscle.

View larger version (170K): [in a new window]   Fig. 10C. —29-year old man with Crohn's disease (same patient shown in Figs. 3A, 3B). G = gluteus muscle. Coronal T2-weighted image obtained 9 months after B to determine whether improvement had occurred after placement of setons for drainage shows fistula (arrow) with internal opening in rectum (R) superior to levator ani muscle (L).

View larger version (169K): [in a new window]   Fig. 10D. —29-year old man with Crohn's disease (same patient shown in Figs. 3A, 3B). G = gluteus muscle. Image from coronal T-2 weighted sequence obtained more anterior than C shows the course of the fistula (arrow) from the recrtum (R) to the left levator ani muscle (L).

View larger version (178K): [in a new window]   Fig. 11. —40-year-old woman with Crohn's disease who underwent multiple surgical procedures several years earlier for perianal fistulas and experienced relapse of disease. Coronal T2-weighted endoanal image shows broad transsphincteric fistula (long solid arrows) with internal opening (open arrow) higher than dentate line (which cannot be visualized on MRI). Inferiorly, fibrous tissue can be seen (short solid arrow). L = levator ani muscle, P = puborectalis muscle, E = external sphincter.

View larger version (120K): [in a new window]   Fig. 12. —19-year-old woman with Crohn's disease. Coronal T2-weighted endoanal image shows small intersphincteric abscess on left with slight extension supralevatorically (curved arrow). From this abscess, gracile intersphincteric tract (large solid arrow) courses caudally into anus with subtle internal opening (open arrow) at approximate level of dentate line. On right, second tract can be seen (small solid arrow) following intersphincteric path just as fistula on left does. C = coil, L = levator ani muscle, IAS = ischioanal space.

View larger version (152K): [in a new window]   Fig. 13. —39-year-old man with complex fistulating Crohn's disease who barely responded to infliximab treatment. Pain was localized at left ischial tuberosity. Axial fat-saturated T2-weighted image shows fistula (short arrow) in right gluteus muscle as well as fistula dorsal relative to ischial tuberosity on left (long arrow). Ischial tuberosity shows bone marrow edema (curved arrow) contiguous with fistula. Pain that patient perceived was probably caused by reactive edema or osteomyelitis of ischial tuberosity.

View larger version (159K): [in a new window]   Fig. 14A. —56-year-old woman with permanent ileostomy caused by Crohn's disease and discharge of pus and mucus rectally that was ascribed to her vast and complex perianal fistulating disease. Digital rectal examination was impossible to perform because of profound perianal pain. During surgery for excision of fistulas, large rectal tumor was revealed. Axial T2-weighted image shows large lesion isointense compared with surrounding fat (solid arrows). Among features differentiating abscess from mucous tumor are presence of stalk (open arrow) and streakiness of structure seen on the fat-saturated T2-weighted images (not shown). G = gluteus muscle.

View larger version (198K): [in a new window]   Fig. 14B. —56-year-old woman with permanent ileostomy caused by Crohn's disease and discharge of pus and mucus rectally that was ascribed to her vast and complex perianal fistulating disease. Digital rectal examination was impossible to perform because of profound perianal pain. During surgery for excision of fistulas, large rectal tumor was revealed. Photomicrograph of microscopic histopathologic specimen of tumor after resection that was found to be moderately differentiated mucinous adenocarcinoma. (H and E, x200)

View larger version (119K): [in a new window]   Fig. 15A. —17-year-old woman with suspected perianal Crohn's disease and clinically proven pilonidal sinus. G= gluteus muscle. Axial fat-saturated T2-weighted image shows perianal fistula (arrow) coursing from anal cleft to dorsal side of anal sphincter (S, arrowhead).

View larger version (154K): [in a new window]   Fig. 15B. —17-year-old woman with suspected perianal Crohn's disease and clinically proven pilonidal sinus. G= gluteus muscle. Axial fat-saturated T2-weighted image obtained more cranially than A shows hyperintense structure (arrow) with no relation to sphincter complex ending blindly in soft tissue of buttock. This structure is most likely pilonidal sinus because no related intersphincteric sepsis can be seen, and lesion is located in midline of anal cleft. Clinical report in which presence of pilonidal sinus in area is mentioned aids in establishing correct diagnosis.

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